The name basically says it all. The mod will highlight any blocks where monsters can spawn
The config file will be created after you run Minecraft at least once with the mod installed. The config file is located int the .minecraft/config folder. In the config file you can change the following values:
- Color of blocks where animals can spawn at day (green), creatures can spawn at night (blue) or any monster can spawn at any time (red)
- Rendering range (how many blocks it checks in each direction)
- Rendering speed in ticks (lower is faster)
- Enable/disable the check of monster spawns
When you're on a slower computer keep the rendering range low and rendering speed high (1 = 1/20 second). The key that turns rendering on/off can be set in the Minecraft key-binding settings.